Lawn mowers, snow throwers, etc. are typical walk-behind, self-propelled machines. A walk-behind, self-propelled machine includes a motor, a plurality of wheels, and a transmission mechanism. The motor drives the wheels to rotate through the transmission mechanism so that the walk-behind, self-propelled machine moves relative to the ground.
The walk-behind, self-propelled machine requires the right wheel and the left wheel to rotate at different speeds during steering. The walk-behind, self-propelled machine is provided with a clutch to enable the right wheel and the left wheel to rotate asynchronously. Generally, the rotation speed of a wheel is greater than the other wheel's. The clutch is also called a differential device. For the typical walk-behind, self-propelled machine with that clutch, when the motor shaft stops rotating, the machine can be pushed forward to make the wheels continue to rotate forward, and the clutch can cut off the transmission between the wheels and the motor shaft. When the motor stops rotating and the machine is pulled backward to rotate the wheel backward, the clutch cannot disconnect the transmission between the wheels and the motor shaft, and the wheels will drive the motor shaft to rotate. At this point where the differential device is in a driving state, a large force is required to pull the walk-behind, self-propelled machine to move backward, which is known as the “lock-up” phenomenon. After the motor stops rotating, in order to disconnect the transmission between the wheels and the motor shaft and in order to make the differential device enter into an unlocked state, the machine needs to be pushed forward to unlock the differential device, then the wheels can rotate freely relative to the motor shaft. Pulling the walk-behind, self-propelled machine backward cannot make the machine “unlocked”, which brings great inconvenience to users.
After the motor stops and when the machine is pushed or is pulled, the wheels will rotate and drive the motor shaft to rotate through the transmission mechanism. In that condition, a great force is required to push or pull the machine to move.